1. Technical Field
The present disclosure relates to a fuel cell.
2. Description of Related Art
A fuel cell is a power generating device which can convert chemical energy into electrical energy through an electrochemical reaction. The fuel cells are usually classified as alkaline fuel cells, solid oxide fuel cells, and proton exchange membrane fuel cells. Recently, the proton exchange membrane fuel cells are rapidly developed and have attracted great interests.
A membrane electrode assembly is an important component of the proton exchange membrane fuel cell and includes a proton exchange membrane and two electrodes. The proton exchange membrane is sandwiched between the two electrodes. The electrode commonly includes a catalyst layer and a gas diffusion layer. The catalyst layer is sandwiched between the gas diffusion layer and the proton exchange membrane. The catalyst layer commonly includes a catalyst, a catalyst carrier, a proton conductor, and adhesive. In general, the catalyst carrier is carbon particles, and the catalyst is nano-scale precious metal particles uniformly dispersed in the catalyst carrier. A catalytic efficiency of the catalyst layer can influence the property of the fuel cell. The catalytic efficiency can be increased by increasing the three-phase reaction interfaces between the precious metal particles and reaction gas, and protons and electrons. Specifically, the reaction gas such as hydrogen can reach the surfaces of the precious metal particles through gas passages and generate protons and electrons from a catalytic reaction. The protons can move toward the proton exchange membrane through proton passages defined by a network composed of the proton conductor. The electrons can transfer toward the gas diffusion layer through a conductive network composed of the catalyst carrier. If the transfer passages are obstructed, the electrochemical reaction of the fuel cell will be frustrated.
The catalyst layer is commonly formed on the surfaces of the gas diffusion layer and the proton exchange membrane by brush coating, spraying, or printing. The catalyst layer has a disordered stack structure composed of a plurality of aggregates. It is difficult to catalyze the electrochemical reaction because the precious metal particles are embedded in the aggregates. Thus, the utilization rate of the catalyst in the catalyst layer having the disordered stack structure is low.
What is needed, therefore, is to provide a fuel cell having a high catalyst utilization rate.